An apparatus for supporting parts of metal barrels is shown in German OS No. 1,931,172 so that a barrel ring and a barrel bottom can be held together at three circularly spaced points by means of support and guide rollers which can be rotationally driven. Such an apparatus can only be used if the hollow members to be rotatably held in this manner are circular and have no significant undulations in diameter because, otherwise, they stick to the support and guide rollers. Further, the support at only three circumferential points permits only inadequate centering and, in particular, prevents nonmutual displacements of the parts to be welded together which might arise as a result of geometrical inaccuracies and thermal expansion. The drive for each support and guide roller is also relatively complicated. The direct rotary drive of the hollow cylindrical members to be welded together leads to the disadvantage, when using stationary centering means, that the hollow members can be rotationally or otherwise displaced relative to one another when the rotary movement is started so that defective welds can occur. When using a relatively large number of support and guide rollers, the cost of construction is high, particularly if it is necessary to form the apparatus so that it is adaptable to bodies of different diameters.
In order to achieve more accurate centering, the use of tension rings is proposed in German UM No. 1,899,244 and UM No. 6,802,044, the curvature of the tension rings being adapted to the circumference of the hollow members to be welded together. Thus, such an apparatus is only suitable for bodies having accurately predetermined dimensions, or else it requires costly and complicated reconstruction for adaption to other dimensions.